The present invention relates to an electric transfer switch unit, and more particularly relates to an electric transfer switch unit provided with a two-position toggle mechanism for selective connection to different power supplies.
An electric transfer switch is used for selective connection between different power supplies. For example, an electric load is connected, via a transfer switch unit, to a normal power supply under normal conditions but connected to an emergency power supply in case of blackout due to earthquakes or floods, etc. On recovery of the normal power supply, the electric load is connected back to the normal power supply through shifting in position of the transfer switch.
In one type of the conventional electric transfer switch unit, a moveable contact is employed for selective contact with a plurality of stationary contacts and an energy storage mechanism such as a toggle mechanism is used for swift shifting of the moveable contact. After the moveable contact has performed shifting in position, the toggle mechanism locks the moveable contact for maintenance of contact with a selected stationary contact.
One example of such a transfer switch unit is disclosed in U.S. Pat. No. 4,590,387. All of the conventional transfer switch units of this type are, however, accompanied with lots of problems. First, the transfer switch units are in general much complicated in construction necessitating use of many mechanical elements. Second, due to use of many mechanical elements, they are relatively large in construction. Third, large distances between stationary contacts necessitate use of a circuit interrupter.
It is the primary object of the present invention to provide an electric transfer switch unit simple and compact in construction.
It is another object of the present invention to provide an electric transfer switch unit which assures reliable operation without need of a circuit interrupter.
It is the other object of the present invention to provide an electric transfer switch unit of low cost and adapted for easy assemblage.
In accordance with the present invention, an electric transfer switch unit is provided with a toggle mechanism for swift selective shifting between two different power supplies such as a normal power supply and an emergency power supply.
The toggle mechanism is used for a transfer switch unit including a moveable contact mounted to a rotatable crossbar. The moveable contact is able to shift between the first and second stationary contacts which are respectively connected to different power supplies such as a normal power supply and an emergency power supply. The toggle mechanism includes link arms for forming a pair of toggle linkages for driving the crossbar, extensible links and coil springs encircling respective extensible links. Mechanical energy for swift shifting operation is stored in the coil springs.
The toggle mechanism further includes a handle mounted to the crossbar. As the handle turns about the longitudinal axis of the crossbar, the crossbar and the toggle linkages are also driven for rotation for intended shifting in position of the transfer switch unit. The handle may be driven for turning by manual operation or by operation of a proper drive unit such as solenoids.
Turning of the handle causes compression of the pair of extensible links and the associated coil springs. Upon turning of the handle over a prescribed angle, the moveable contact is made to shift by rotation of the crossbar from a closed position with one stationary contact to a neutral open position. Thereafter, as one pivot of the extensible link traverses a straight line connecting both pivots of the extensible link to the longitudinal axis of the crossbar, the extensible links and the coil sprigs are extended and release stored energy for swift rotation of the crossbar. Next, the moveable contact carried by the crossbar shifts to the neutral open position to a closed position with the other stationary contact so that the moveable contact is brought into electric connection with the other stationary contact. Since a large distance is reserved between the moveable contact and the stationary contact for reliable insulation, no use of current interrupter is necessitated.
The coil springs store energy until one pivot of the extensible ling traverses the straight line connecting the both pivots of the extensible link and the longitudinal axis of the crossbar. Consequently, the handle is locked by the toggle linkages in order to inhibit separation of the moveable contact from the stationary contact. Thus, the toggle mechanism inhibits accidental separation for the moveable contact from the stationary contact due to possible application of mechanical or electric external forces.
In the closed position, the moveable contact is urged for reliable contact with the stationary contact thanks to operation of the coil springs.